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Astrophotography

Small Asteroid 2014 AA Hits Earth

Discovered on New Year's Eve by a telescope in Arizona, a small asteroid struck Earth somewhere over the Atlantic Ocean — apparently unnoticed — about 21 hours later.

A sequence of four images, taken roughly 9 minutes apart, reveals the movement of asteroid 2014 AA when it was discovered in northern Orion early on January 1st (Universal Time). The 19th-magnitude object struck Earth 19 hours later. The field of view is about 5 arcminutes across.

Catalina Sky Survey / NASA

It was New Year's Eve, but that didn't stop observer Richard Kowalski from scanning the sky for near-Earth objects (NEOs).

He hadn't been using the 60-inch telescope on Arizona's Mount Lemmon for long when he noticed a 19th-magnitude blip skimming through northern Orion in a seven-image series begun at 11:18 p.m. MST (6:18 Universal Time on January 1st). After confirming that it was a new find, Kowalski dutifully submitted positions and times to the IAU's Minor Planet Center. Then he went back to the night's observing run.

Thus did the Mount Lemmon reflector, part of the Catalina Sky Survey, discover 2014 AA, the first asteroid found this year. But at the time neither Kowalski nor anyone else realized that the little intruder was only 300,000 miles (500,000 km) from Earth and closing fast.

This plot shows the range of possible locations where the small asteroid 2014 AA struck Earth's atmosphere early on January 2, 2014.

Bill Gray / Project Pluto

As announced by the MPC earlier today, it's "virtually certain" that 2014 AA hit Earth. According to calculations by dynamicist Stephen Chesley (Jet Propulsion Labo­ra­tory), the impact occurred somewhere between Central America and East Africa. Chesley's "best-fit" collision is over the Atlantic Ocean just off the coast of West Africa at roughly 2:30 Universal Time this morning.

More precision has come from an analysis of infrasound data by Peter Brown (University of Western Ontario). Infrasound is extremely low-frequency acoustic energy (20 hertz or less) created, for example, during energetic explosions. A global network of detectors, maintained by the Comprehensive Nuclear-Test-Ban Treaty Organization, can pinpoint the location and energy of any powerful detonation — including airbursts from meteoric blasts.

The overlap of the white curves, from three marginal infrasound detections, shows where the small asteroid 2014 AA likely hit. However, this preliminary plot does not take winds into account, which might shift the true impact point somewhat further east.

Peter Brown

According to Brown, 2014 AA triggered very weak detections at three infrasound stations. His triangulation from those records, shown in the graphic at right, indicates that the space rock slammed into the atmosphere near 40° west, 12° north. That location, about 1,900 miles (3,000 km) east of Caracas, Venezuela, is far from any landmass.

"The energy is very hard to estimate with much accuracy — the signals are all weak and buried in noise," Brown explains. And yet, he adds, we're lucky that the event happened just after local midnight, when winds are calmest. "Had this occurred in
the middle of the day I doubt we would see any signals at all," he says.

Brown's rough guess is that the impact energy was equivalent to the explosive power of 500 to 1,000 tons of TNT — which, though powerful in human terms, implies the object was no bigger than a small car. "It was no Chelyabinsk," he says.

So 2014 AA was too small to reach the ground intact. But it must have created one heck of a fireball! The skies over the Atlantic were relatively clear last night. Alas, a search of ship- and plane-tracking websites turned up no vessels in that area — it seems that no one was positioned to witness 2014 AA's demise.

"I'm not aware of any visual sightings," says William Cooke of NASA's Meteoroid Environment Office in Huntsville, Alabama. "Looks like it was too far away from human eyes."

The impact occurred a little after 3h UT, Brown says. That's only about 19 hours after Kowalski's initial report to the MPC, and it's giving me déjà vu all over again. It's been just five years since another small asteroid called 2008 TC3 struck Earth over Sudan just 19 hours after its discovery by the same telescope.

The difference between these events is that astronomers had nearly a day of advance warning regarding the 2008 impact. Telescopes worldwide amassed hundreds of observations before the object slammed into the atmosphere, and eventually many fragments were recovered.

Based on images taken in the hours before its impact, asteroid 2014 AA averaged 110 million miles (175 million km) from the Sun in a low-inclination orbit that crossed paths with Mars and Earth. It was only a matter of time before it encountered our planet. Click on the image for an interactive version.

JPL Horizons

There was no heads-up alert this time. "I'm kicking myself for not having spotted this," admits amateur NEO sleuth Bill Gray (Project Pluto). Most mornings Gray downloads "and yes, for me, it was holiday-related."

Most mornings, he downloads the circumstances for recent discoveries and computes "what ifs" for potential impactors and near-misses. "However, on New Year's Day, I'd made arrangements to go with my family to visit my sister, go for a walk, stop off for a doughnut, shovel snow, etc., etc." He didn't realize an impact was imminent until last night — only a couple of hours before the impact.

Let's cut Gray some slack and instead give him, Chesley, and Gareth Williams at the MPC a collective pat on the back. All three were able to conclude — based on just seven images taken within 69 minutes — not only that 2014 AA was going to strike Earth, but also roughly where and when. Mad props for that impressive number-crunching!

Asteroid v Meteorite, what is the difference? Why is this rock categorised as an asteroid & not a meteorite?

Whatever it is classed as we had a lucky escape! If it had come down over a inhabited region, like the Russian one last year (even if it wasn’t as big!), the bang would certainly have rendered the firework displays mute!

Congratulations to Rich Kowalksi !!
Love the story, Kelly.
Question: As an long time owner of a 12 inch "Cat" telescope, I spend a lot of nights "looking up". How does a person get involved in the sport of "Asteroid Hunting"?
I am ready to dedicate some time to this endeavor.
Thanks
Raymond

The reason I came across your findings was due to an unexplained object flying through the sky. On January 1st at 07:24pm on highway 101 in Lower Sackville, Nova Scotia, I saw what looked to be a large red ball of fire moving across the sky. It was moving slow enough for me to point it out to my fiancé while I was driving. Unfortunately, it was moving fast enough to be out of sight within 5 seconds. We both sat there discussing the possibilities. It was too close and too slow to be a shooting star, it wasn’t an aircraft, and it wasn’t a firework. So I googled asteroids in 2014 and read this. I just wanted to let you know that at least two people witnessed your asteroid.

Perhaps 2014 AA had a twin traveling at some distance? Or else you might have seen another coincidental meteorite on the same date as 2014 AA; reminiscent of that which we experienced on the day of the Chelyabinsk event in Russia?

I have a small problem with this report of the discovered 19th mag object being the same as the impact object. If an object is thrown at me it doesn’t move much in my view, it just keeps getting bigger. This discovered object was moving quite a bit in each of the 11 minute exposures. I find it hard to believe the object moving left to right, across your FOV at 300,000 miles at the time of the sighting, is going to impact anywhere within 20,000 miles of your position. Great story, but makes me think this is more sensationalism than accurate news.

I live in New Orleans and I was outside actually watching fireballs fly through the sky. I have a few pictures of this eevent. So another sighting of this event was seen in Louisiana and my family has pictures from this in California. They were impressive and extremely fast fireballs flying about the height a plane would fly.

Some comments here mentioned other sightings of fireballs. These are almost certainly unrelated. Small fireballs, bright enough to be locally spectacular (the sort of thing that makes you say, "wow! what the heck was that!") are surprisingly common. There are hundreds every day globally. An object a couple of meters across, like this tiny "asteroid," disintegrates in the Earth’s atmosphere roughly once a day (or maybe every five days depending on how you define things). And something this size can be dazzlingly bright and will cast shadows on the ground as it dumps its energy in the atmosphere. It’s too bad no one saw it. But 70% of the Earth is ocean, and most of the Earth’s land has very low population density. So the vast majority of these visually spectacular fireballs go unobserved. But things are changing… Within a decade, we may reasonably expect that half of these super-fireballs will be detected with enough advance warning that we might at least be alerted a few hours in advance. Enough time to run outside and enjoy the show. Another benefit of the Information Age…..

Dear S&T web site team, You folks are losing out by limiting the initially displayed comments to just TEN. Very few of your readers will spot the "Read All Comments" button and realize that this leads to more messages. How about showing the first 25 or even 50 comments on the top page? It’s an easy coding change (even a consultant shouldn’t charge you for it!).

We’ve got categories of planets: gas giants, terrestrial planets, and now dwarf planets. We need some categories below those to separate the asteroid wheat from the asteroid chaff. Obviously, this object, 2014 AA, qualifies by minimal standards as an "asteroid" because it was discovered as asteroids are normally discovered, and it was handled by the MPC. Therefore, "asteroid". Unfortunately for public communication, this term is far too broad. This tiny asteroid was NOTHING compared to the Chelyabinsk object (if this one was 2 meters in diameter and the Chelyabinsk meteor was 20 meters in diameter, then assuming similar density the latter’s energy was 1000 times greater). While it was numbered as an asteroid, this should be referred to as a "meteor" or perhaps a "meteor detected by an asteroid survey". By the way, it’s still worth mentioning the amazing New Year’s coincidence: you discover the very first new "asteroid" of the year (though it turns out it’s just a small meteoroid) and it’s gone in a day because IT HIT THE EARTH. What are the odds?

I live at 32.5N 81.9W .I heard a loud boom in he sky late one night near new years eve. It may not have been this event but a precog impression of it. Who knows? There are all kinds of communications going on in the universe. Get tuned.

Frank, you make a very good point. Many of my non-astronomer type friends are very surprised when when I tell them there is no precise diameter to distinguish meteoroids from asteroids. It seems if the object is more than 1 meter we could call it an asteroid. I then expain that we can’t calculate a prcise diameter because we do not know the albedo (the percentage of light the object reflects) and that some asteroids are very dark (Carbon chondrites) but others can be very bright etc. I have often thought that an object with an absolute magnitude of more than 31 should be a meteoroid and less than 31 (and thus brighter) should be an asteroid. (The absolute magnitude of an asteroid is its magnitude if was 1 AU from the sun and 1 AU from the earth, which can be calculated since we know it apparent magnitude and its distance from earth using the inverse squar law etc.) However, even this does not work for 2014 AA. 2014 AA has an absolute magnitude of 30.944 which according to my definition of an asteriod, since it is brighter than 31. …but wait – that measurement has a standard error of .11986 which means there is about a 30% chance it is faint enough to be a meteoroid and about a 70% chance it is bright enough to be an asteroid. So using the object absolute magnitude to tell if it is an asteroid or meteoroid will not work for object close to magnitude 31 either. I guess we will just have to keep using the definition,if it is telescopically discovered it is an ansteroid. Does anyone have a better idea ?

a 2010 paper by Alan Rubin and Jeffrey Grossman (http://is.gd/uF62nd) does in fact state that “meteoroid” should be used for objects no bigger than 1 m across. as Bill Watson points out, it’s hard to know an object’s true diameter based on brightness alone, but his threshold of H = 31 is close to objects being +/- 1 m across — though based on this table (http://is.gd/AurjCq) I think H = 32 might work better.

Thanks to everyone who tried to give a definition about the difference between a meteor & an asteroid. It was very interesting to read your replies.

I’ve done a small search on The Free Dictionary page, in the Encyclopedia tab, I came across this info which is about as good a definition as can be hoped for:

"In 1961, the International Astronomical Union defined a meteoroid as "a solid object moving in interplanetary space, of a size considerably smaller than an asteroid and considerably larger than an atom".[10][11] In 1995, Beech and Steel, writing in Quarterly Journal of the Royal Astronomical Society, proposed a new definition where a meteoroid would be between 100 µm and 10 meters across.[12] Following the discovery of asteroids below 10 m in size, Rubin and Grossman refined the Beech and Steel definition of meteoroid to objects between 10 µm and 1 m in diameter.[2] The smallest asteroid ever discovered (based on absolute magnitude) is 2008 TS26 with an absolute magnitude of 33.2,[13] and an estimated size of 1-meter.[14] Objects smaller than meteoroids are classified as micrometeoroids and cosmic dust. The Minor Planet Center does not use the term "meteoroid"."

Note: the International Astronomical Union (IAU) defines a "meteoroid" as being in orbit around the Sun. The IAU, knowing that a "meteoroid falling through the Earth’s atmosphere" is no longer orbiting the Sun, has defined a "meteor" as being the extraterrestrial object, as well as, the "visible streak of light" that it produced. The relegating of the term "meteor" to being only the "visible streak of light" is a common misuse of the terms "meteoroid" and "meteor" as originally defined by the IAU.
From Asteroids to Meteoroids to Meteors to Meteorites
An Article In Meteorite-Times Magazine
by Robert Verish

We know that NEOs pose a serious risk, and are taking steps to make sure a big one doesn’t sneak up on us. But as the lucky people of Chelyabinz (I’m serious! I would’ve loved to have been there!) learned, an asteroid doesn’t have to actually strike the ground to cause tremendous damage, injuries, or even fatalities. The asteroid that obliterated the forests of Tunguska didn’t hit the ground either.

Sorry, size does matter! By definition,an asteroid is a rocky/metallic object orbiting the sun that is greater than 10 meters in diameter, yet smaller than a dwarf planet. A meteoroid is less than 10 meters in diameter.

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